Buzzing noise

Hello, I have a 2007 Mac Book Pro running all of the latest software. However, recently I have been hearing very loud buzzing noises that sounds like a swarm of bees coming from the back left of my computer right near the speakers. I'm fairly certain that it is either the hard drive or the fan because I don't know of any other parts moving fast enough to make a buzzing noise in that area. It had been happening usually once or twice per week originally a simple reboot used to do the trick, but since the beginning of today no amount of restarting seems to fix it.. In fact it is even buzzing right now while I type this message. My warranty expired a while ago and I don't want a new computer so if there is anything I can do to fix this that would be great. If not, I can take it to the apple store and see what they can do. So any help is appreciated.

Thanks!

Edit: Two more things -

1.) Closing and opening my computer fixes the problems for 30 seconds to a minute until it starts back up again.

2.) iStat Pro says that my right fan is rotating usually between 6 and 8 times faster than the left fan while it is buzzing. The left fan is at about 600rpm while the right fan is usually at 3,000-5,000. However, for the 30 or so seconds while my computer is back to normal they even out at about 3,000rpm each.

What do you think could have caused it? I noticed that it started happening when my laptop was cold so maybe the metal started to contract and the fan started scraping against it which then caused further damage, but that still doesn't explain why the other fan is perfectly fine, why it is only buzzing some of the time, and why there is such a difference in speed between the two fans.

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